RE: Fav. Urban Legend...

From: John Kanagaraj <john.kanagaraj_at_hds.com>
Date: Tue, 12 Mar 2002 13:58:24 -0800
Message-ID: <F001.004263A4.20020312135824@fatcity.com>

>I'm doing Oracle Urban 

> Legends. I've got
> several in my presentation but I thought I'd ask here, before
> I put the
> presentation to bed, what your favorite (or the one you find the most
> irritating) Oracle Urban legend was....

Robert,

I believe Jeremiah Wilton presented on a similar topic at OOW. When asked for inputs, mine was as below:

• You *have* to take a COLD backup of the database after using resetlogs. (Not required - a Hot backup and archive logs is adequate. All hot backups / archive logs prior to that are invalid, though...)
• You *have* to create an additional Rollback segment in the SYSTEM tablespace before creating *any* object in a tablespace other than SYSTEM (even additional Rbs in a non-SYSTEM tablespace). This used to be true in V6 and before, not anymore.
• Backup the online redologs along with the datafiles/controlfiles in a Hot backup (Disaster strikes when the redologs are restored on the current online redo logs!!)
• Continuously run ALTER TABLESPACE COALESCE
• Allocate different values of INITIAL/NEXT extent sizes for large objects depending on the 'expected growth pattern' - this makes sure that the number of extents for large objects is kept down. (Sheesh!)
• COMPRESS=Y during Export compresses the extents into 1 huge extent, and that's GOOD!
• Make sure that all your Tablespaces have at least 15% (or whatever) free (i.e. stress the percentage rather than making sure that the largest free fragment is larger than the largest NEXT extent at the least)
• You are absolutely protected from Redolog file corruption by hardware multiplexing it. (i.e. What if you fat-fingered an online redolog?)

I might have added more on Tuning and Performance, but Gaja has already exploded all those myths!

One thing I will note though - there's bound to be lots of fire and flak erupting in your presentation. There are *lots* of so-called experienced DataBase Baby Sitters out there fed exclusively on 'Oracle for Dummies' books who had adopted these myths as reality and will be prepared to defend their position. You will need documented evidence in the form of logs or timings to make your stand for exploding some of these myths.

I am sure that others would add to this! (and I note that the 'lots of extents is bad' myth is already noted!)

John Kanagaraj
Oracle Applications DBA
DBSoft Inc
(W): 408-970-7002

Grace - Getting something we don't deserve Mercy - NOT getting something we deserve

Click on 'http://www.needhim.org' for Grace and Mercy that is freely available!

• The opinions and statements above are entirely my own and not those of my employer or clients ** -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: John Kanagaraj INET: john.kanagaraj_at_hds.com

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